1. Field of the Invention
The present invention relates to a dielectric substrate and a device that utilizes the electric substrate, such as a waveguide or a transmission line transition.
2. Description of the Related Art
Usually, a waveguide tube is formed of a plural dielectric substrates (only one illustrated in FIG. 8) each of which has a hole or a cavity (H). The peripheral wall of the hole is coated with a conductive film, as disclosed in JP-P3347626. When manufacturing a waveguide tube, conductive ink is printed on the peripheral wall to form a conductive film. However, it is difficult to form a flat conductive film due to the surface tension thereof as shown in FIG. 8. Further, an uneven surface of the conductive film that is formed on the peripheral wall may degrade the performance of the waveguide tube.
On the other hand, an array of plural via holes or through holes may be formed as a peripheral wall of the hole instead of the conductor film, as disclosed in JP-P2001-196815A. The array of via holes must be formed on the dielectric substrate at a certain distance (e.g. 0.5 mm) from the edge or the peripheral wall of the hole in order to secure the mechanical strength thereof. However, this distance may also degrade the performance of the waveguide tube.